M172 - Sweep Drive/Dac - Wavetek 3000 Instruction Manual

,PF FROM
/Yl9 kv
PIN
O/OOE
ATTENUATO .q
"S UNG FVEL EO "
L AS NT
0.4l VER
TO L /LINT ON
MJETENP B0 .4k'D
3 .8 .3
"Unleveled" Light Driver
3 .9
M172 - SWEEP DRIVE/DAC
WlOE BANp
AMPG l FlEQ
401r1-EREN7- 1A1
AMP
When the differential amp in the leveler
circuit is putting out a voltage which
would cause the PIN diode attenuator to
be at its high or low resistance limit,
the leveling circuit can no longer be
effective . The above voltage levels,
which are applied to the unlevel light
driver, are adequate to turn on a source
of current for the indicator which ap-
pears through the front panel .
This module provides two output voltages .
One is linear from 0 V to -5 V as the
frequency goes from 0 to 39 MHz, re-
peating every 40 MHz ; the other varies
from +7 V to -8 V as the frequency goes
from 0 to 520 MHz . The second voltage
is shaped to linearize the VCO in the
M9W Sweep Oscillator .
s
(''EFERENCE)
L E VEL
CONTROL
F .QOM /LIFTER BGARO
Figure 3-13 . M10W - Output Amplifier
THEORY OF OPERATION
lwCi/Vl TO.Q
OIOGE
-~ O4/~rPUT
MO
AASSIYE
STEP ArrrArkA1TOR)
Two digital-to-analog converter ICs,
programmed by the front-panel Lever/
Indicator switches, provide the 0 to 520
MHz voltage . This is shaped in the next
section of the module . A third DAC pro-
vides the repeating 0 - 40 MHz voltage .
Since the state of the 20's line depends
on the 100's line, the 20's line is in-
verted when the 100's line is high .
The analog tuning signal from the M172
is "shaped" before driving the M9W wide
oscillator . The shaper is an inverting
DC amplifier which amplifies the input
by a smaller factor for smaller magni=
tude inputs . Shaping this analog voltage
compensates for the non-linear change
in capacitance of the varactor diodes
in the oscillator circuit .
3-13